This invention relates to structural components of fire doors. In particular, the invention relates to structural components, such as stiles, rails, and edge banding, formed of fire-resistant materials, to a method and to a dry mix for making these components, and to fire doors comprising these components. The structural components provide structural strength sufficient for attachment of fittings and hardware by use of standard carpentry techniques.
The use of fire doors in buildings is an important factor in avoiding injuries and loss of lives and in preventing property damage as a result of their ability to deter the spread of fire. In the interest of public safety, standards have been set by governmental agencies, building code authorities, and insurance companies for the installation and performance of door assemblies that retard the passage or spread of fire. Building codes require that fire-resistant door assemblies be installed in wall openings and that such assemblies pass standard and industry-wide accepted tests that are an evaluation of the fire-resistant properties of the door assembly.
The fire door contemplated by the present invention is a composite structure comprising a manufactured fire-resistant core surrounded by an edge frame or banding, and, optionally, other features, and having veneer or other sheet surface coverings usually comprising either wood or plastic. Such a composite door must have certain basic properties in order to meet accepted standards and pass industry-wide accepted fire endurance tests of door assemblies in accordance with ASTM E-152. In these tests, the door is exposed to intense heat such as that generated by fire in a burning building. Exemplary conditions of such tests involve exposing the door to temperatures that progressively increase to values within the range of 1750xc2x0 to 1800xc2x0 F. for an exposure period up to 1xc2xd hours.
Manufactured fire door cores are known in the art. Typical of such cores are those made of calcium silicate, often together with asbestos and Portland cement. As such cores have fallen from favor in view of the safety and environmental concerns related to the presence of asbestos, cores based on gypsum were developed. However, door cores comprising significant proportions of gypsum often have a relatively high density, thus yielding relatively heavy doors. U.S. Pat. No. 4,159,302 and U.S. Pat. No. 4,343,127 are directed to gypsum-containing cores that have reduced density yet satisfy fire code requirements.
Typically, cores are manufactured by introducing a mixture of materials in a moldable state into a mold. Skilled practitioners recognize that such moldable mixtures typically include water for hydration of components such as cements and gypsum, and may include additional water to make the mixture easier to transport as a fluid. Excess water must be removed after the desired shape has been achieved. Then, edge banding and similar features are attached after the core has been dried. The cores disclosed in U.S. Pat. Nos. 4,159,302 and 4,343,127 were manufactured with a minimum quantity of water, thus obviating the need to press water out of the mixture.
Edge banding often is used in doors having such manufactured cores because the core materials, whether made with a minimum quantity or excess quantity of water, do not exhibit the strength required to hold screws and other fasteners, and are not resistant to splitting. Such fasteners are necessary to attach hardware, such as hinges and other devices, to the door. Known banding typically is dense, and therefore adds significantly to the weight of the resultant door.
Thus, there exists a need for structural components for a fire door meeting the fire code requirements and also providing convenient and economical manufacture and simple and effective fitting and mounting of the doors by use of standard carpentry or other conventional tools.
There also exists a need for a composite door formed of a molded core and composite edge banding made up of a plurality of strips of fire-resistant materials, and having not only good fire-resistance and strength characteristics so as to reinforce the edges of the core and to meet conditions of use, such as door slamming, but also exceptional integrity and machineability.
The invention is directed to structural components for a fire door meeting fire code requirements, to a method for making such components, to a dry mix for making such components, and to the resultant fire-resistant door comprising the structural components. The structural components are formed from fire-resistant compositions that are press molded from moldable compositions. The components are less dense than known components, yet have screw-holding strength sufficient for attaching hardware and fittings to the door with conventional tools and techniques. Structural components of the invention have exceptional integrity and machineability.
The invention also is directed to a dry mix for making structural components of the invention, and to a method for manufacturing the structural components of the invention. In accordance with the method of the invention, the dry materials used to form the composition are moistened with a quantity of fluid, typically water, sufficient to provide that quantity of water necessary to satisfy the hydration requirements of the composition, and to provide a damp mixture sufficient to facilitate formation of the components during the molding process. Thus, the moldable composition is easily formed into the desired shapes and compression molded, yet has a green strength sufficient to enable transfers and handling of the components essentially immediately after being formed. The structural components also are easily incorporated into a fire door.